


Core

by Gothfoxgirl



Category: Undertale (Video Game), 僕のヒーローアカデミア | Boku no Hero Academia | My Hero Academia
Genre: Abused Midoriya Izuku, Abusive Midoriya Inko, F/F, F/M, M/M, Midoriya Izuku Does Not Have One for All Quirk, Midoriya Izuku Has Multiple Quirks, Midoriya Izuku Has a Quirk, Not Beta Read
Language: English
Status: In-Progress
Published: 2019-05-08
Updated: 2019-06-21
Packaged: 2020-02-28 15:39:11
Rating: Not Rated
Warnings: Graphic Depictions Of Violence, Underage
Chapters: 2
Words: 3,662
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18759370
Author URL: https://archiveofourown.org/users/Gothfoxgirl/pseuds/Gothfoxgirl
Summary: Magic. It once flowed through the planet, soaking it with its power. But, what will the planet do with someone that can use it after so long and so well. How will they define this quirk? Will it be one or many?When the souls of those thought long gone come back to help a, once, quirkless boy, how will the system be turned on its head?





	1. Magic

Yagi Toshinori crawled out if the sewer systems, as he heard the villain capture someone. Someone young. Just as he was about to call out his catchphrase, he heard music and some kind of blast going off. As soon as he got up there, he found a boy, most likely in middle school, on the ground, coughing up sludge. His hair was shifting from a pale green to a darker shade that was almost black. He sat back and rubbed the tears and saliva from his face, as it looked like his figure started filling out to a normal weight.  
“Shounen? Are you alright?” He nodded and opened his green eyes, taking in a final heave of air to calm his pattern.  
“Y...Yes...Thank you…!” That was when he realized who he was. The blonde groaned internally. This kid was gonna go fanboy. He didn’t expect the kid to look _afraid_. He looked like his heart rate had gone up a little.  
“Shounen? Are you alright? You look terrified.”  
“Am I...going to jail?” Blue eyes blinked in surprise.  
“Why would you?” He looked away, obviously jumpy.  
“I-I used m-my quirk…” Toshinori tilted his head.  
“You used it in self defense. It’s legal to use your quirk to protect yourself.” Something was wrong. Those were the eyes of a person much older, but with tinges of that of a child. The greenette looked away.  
“But...But, my mom said we aren’t allowed to use our quirks no matter what. Only heroes and professionals can.” Toshinori’s smile was gentle, knowing that the flamboyant act wouldn’t do well for this situation.  
“Well...She’s misinformed. It’s legal to use your quirk if you’re in danger. You’re in no trouble, Shounen.” He tried to be as delicate as possible. The kid seemed panicky. 

As the teen calmed, he noticed that the villain had been almost all vaporized. What kind of quirk…  
“Mr. All Might?” He looked back to the greenette and crouched even lower, coming to kneel on the ground.  
“What is it?” His time limit was nearing its end, he could feel it. But, this kid didn’t need him darting off in the middle of a panic attack. He just needed to hold out.  
“Is...Is it possible for me to be a hero? Even...Even with my freaky quirk?” The hero was confused.  
“Freaky?”   
“It has different parts and...and there are voices that tell me how to use my abilities...The...The best way to explain is that I can use something like magic...um…”  
“Can you demonstrate?” He looked a little nervous, but closed his eyes. Music started to play, as his appearance changed drastically. He had white hair and was very skeletal looking with black eyes that had white pinpricks in them. He held his hand out to the ground in front of him, making a small forest of bones rip up out of it, but not tearing up the concrete. A blue mist smoked from his left eye, as a huge skull of, what looked like, a dragon appeared out of thin air, its eyes glowing an ethereal blue that put his own to shame. He couldn’t help the awe that came out his mouth.  
“Woah…” The bottom jaw was split, so the underside of the mouth cavity was empty, and the largest of the teeth were length and width of Toshinori’s full arm. They looked sharp and dangerous, yet this thing didn’t need to eat. That was apparent by the lack of most of a bottom jaw or a body to fuel. It disappeared and the teenager wiped his brow of the bit of sweat forming there. He faded back to his normal coloring.  
“So, you have other abilities?” He got a nod.  
“I have ten other sets of abilities, though a couple are really close to the same thing, and the ability to see and find these star-like things that give me ‘save points’ to go back to if something happens. Also, I have a cluster of single powers.” The blonde could only stare.  
“You have more than one quirk?”  
“Not really...It all deals with aura manipulation, so...I don’t think they’re separate…” He realized he hadn't answered the boy’s question.  
“I believe you can be a hero. You can do anything you set your heart to.” The boy seemed to lighten up a little and gave a bow.  
“Thank you.” Toshinori nodded and stilled, feeling the blood come up his throat. 

He covered his mouth with his hand, but he couldn’t turn in time for the teenager to not see the blood seeping through his fingers. Without even an exclamation of surprise, he stepped forwards, his eyes glowing a bright green and spilling a light green fog. His hands glowed the same color, as he put his palms directly where his scar was. He felt no more pain. Only discomfort.  
“Shounen?” His eyes looked distant.  
“How are you even alive? With… _this_...you should be dead…”  
“What?”  
“I can see your injuries. I cannot heal them, but I can dull the pain and give you more time in this form.”  
“?!” Those eyes flickered through every color of the rainbow, before staying on green again.  
“I...I’m sorry. My question kept you in this form too long…” He turned away and scratched at his arms, leaving pink lines over his skin. Toshinori noticed that the rest of the villain was missing, bt he was sure that, with what little part of his body was left, he wouldn’t be too hard to capture. Lifting this boy up, he leapt to the roof of the nearest building. As soon as he touched down, he let go of the boy and smoke billowed around him, leaving him in his, emaciated, base form.  
“I chose to stick around, Shounen. It’s not your fault…” The boy blinked, before facepalming.  
"S-Sorry...I'm Midoriya Izuku." The man shook his hand.  
"Since you've seen this form...Yagi Toshinori." The greenette gave the smallest of twitches of the lips.  
"D-Don't worry. I-I won't say anything to anyone."  
"Thank you-!" Suddenly, an explosion went off in downtown.   
"K...Kacchan?" That's the first thing that came to mind, knowing of only one person that had an explosive quirk.

In seconds, the boy was at the stairwell, before the blonde could call out to him. He reached the middle of town by shifting into that white-haired form and teleporting to an alley in the square. The sludge villain had reformed most of his body and had Kacchan trapped. _Kacchan was trapped._ Now, he doesn't particularly like the guy, but he's been one of the only ones to actually give him any sort of attention...and they'd once been friends. He couldn't let him suffocate. No...He couldn't let _anyone_ suffocate! He noticed the heroes around and they weren't doing anything. They weren't trying to save a teenager on the verge of choking to death. Izuku felt his blood boil. Even if they weren't the best suited for it, they should be trying! His hair turned a blood red, growing to his waist, while his teeth turned sharp and his eyes faded into a honey amber color. He felt his magic bubble through him, before a spear of aqua energy appeared from his hand and shot for the villain, impaling one of his eyes and ripping enough sludge away to allow the ash blonde to breathe. A, high entry, song started to dominate from him. He leapt in, his teeth bared, as he put his hand out. Glowing, light blue, dots appeared on the ground, before the spears burst from the ground, hitting the sludge, but not Katsuki. His voice came out, mixed with that of a tough-sounding, woman.  
"Didn't get enough when ya caught me, did ya, Punk?!" He didn't give the villain time to respond, as one of his eyes glowed blue. Something heart shaped in Bakugo's chest turned blue and he was pulled from the goop, set down back with the heroes, who rushed to see if he needed to go to the hospital. He swore at them that he was fine. Izuku gave a cocky smirk, as the sludge found himself unable to move, the heart green in his chest. Izuku's eyes flickered back to blue again, as he encased the villain in a cage of glowing light blue bones.  
"Don't try to escape. You'll have a bad time." There was a thump from the inside, before a yell of pain filled the air.  
"Told ya, Pal." He turned on heel, as his appearance changed to the white haired one, and approached the heroes.  
"Spare me the scolding and get that guy. I can't drop my quirk without the bones leaving too." As the heroes surrounded the construct, he snapped his fingers, letting the bones fade. As the color came back to his face and his weight evened out, he heard the ashen blonde speak under his breath.  
"...Deku?" He glanced to him, his eyes changing to green from the white pinpricks they were. He didn't look again, as he disappeared into the crowd with little more than a stiff wave. 

He was a block and a half from his house, when he had someone running after him. He flinched and saw that it was Toshinori.  
"Oh...It's just you…"   
"Shounen, that was amazing. You rushed in without a second thought! There's no doubt in my mind that you can be a hero! If you'd accept, I'd like to make you my successor!" Izuku blinked.  
"Successor?" Toshinori explained his quirk and what had happened to him.  
"I...I see, but I can't. I mean...my quirk is already super strong. I...I don't want to have a one-up on the others right off the bat...I-I'm sorry." The blonde nodded.  
"I understand. But...May I, at least, train you? You seemed to have a good grip on your quirk, but I could see the exhaustion you exhibited afterwards. I think I can help you with that." The greenette stared at him.  
"What would you get out of it? What would make it worthwhile to you?" The hero started. What kind of kid thinks of that?  
"Well...Other than feeling like I'm doing som good, I guess...I was hoping this would help me get better at being social and, maybe...maybe get back in shape in this form." Izuku's eyes glowed a dark blue for a moment.  
"You tell the truth...I...I accept." The man smiled and they swapped numbers, before agreeing to meet at Dagobah Beach that weekend. 

As Izuku rounded the corner of his street, he felt a pit of dread spread through his stomach. That incident had been broadcasted live across the network. There was no doubt that his mom had seen it. He walked through the door and tried to make it to his bedroom without making his presence known. He failed. From the living room came Inko, obviously drunk. She saw him and made a beeline. He stilled and looked to the floor, knowing she'd get angry if he met her eyes. He didn't flinch, as she brought her hand across his face, hard. He said nothing. He made no motion that it stung. He just let her drunkenly mumble about her getting caught, because Izuku thought playing hero would be fun. Luckily she was too drunk to do more, so he slipped into his room to do his homework.

A single tear hit the desk and he rose his shaking fingers to his face, finding a wet trail seeping from his right inner corner. He grimaced. He just wanted a normal life.


	2. Learn To Live

**Notes for the Chapter:**

> Jesus....This took forever and so much will to go back to XD Now that it's past this point, I think i can keep going on it...hopefully

It'd been a couple months since they made their agreement. A couple months of hauling trash off the beach. When he had the boy sit, he noticed the scars that littered his body.  
"Midoriya-shounen? You're only fourteen. How did you get so scarred up?" Shit. Izuku hid his panic and sighed.  
"I was, and am still, a clumsy kid. I run into and fall off of things all the time." Toshinori knew it was a partial truth. How would a kid get that kind of scar across his mid back by falling? The teen stretched, showing off the scar in question even more. It looked like someone had taken a rake to his back. 

"Alright. Um...How many parts of your quirk are, well...technically separate?" The strange sounding question was answered by the boy looking like he was counting.  
"...Seven. Kindness, Patience, Integrity, Bravery, Justice, Perseverance, and Determination. They give me a boost in certain things like mental capacity or drive and some produce weapons or shields."   
"Which ones produce physical things?"   
"Well they all can produce weapons, but some are more suited for other things. Kindness manifests frying pans for some reason and grants me healing abilities. Patience broadens my mental capacity and creates small daggers. Integrity is more of an ability to know if someone's lying and produces a shield or barrier around me. Bravery is a boost in drive and makes boxing gloves that I can either wear or use as a separate attack. Justice gives me the ability to know a person's alignment and manifests pistols. Perseverance helps me focus and is the only ability that allows me to directly focus my magic on certain things through giving me a spellbook. It's kinda like the book series Harry Potter. Determination...is the most potent. It gives me a boost in energy, mana, and magic and it can produce two things. Huge knives or…a...a blood red scythe…"   
"Shounen?" The greenette turned...afraid and apprehensive. He sighed.  
"I think I should tell you where this comes from…I...I'm actually quirkless." The blonde stared at him in utter shock and the definition of confusion.  
"What?"   
"I was born to be powerless. All these abilities come from souls."  
"Souls?" Those green eyes looked away.  
"I know...I know you're gonna look at me like I'm crazy, but...These individual abilities come from eight human souls. Six of which were murdered. One killed herself. And one lived out her life, having freed the others...The other source of my abilities. The souls of eleven, technically twelve, monsters...Don't...Don't look at me like that...Don't look at me like I'm out of my mind…" Toshinori could only blink.  
"Monsters?"   
"They've been extinct for a couple hundred years...but yes. Monsters. Not the kind you'd think of, though. There was a whole community that lived in North America. They lived, hundreds of them, under a mountain known as Mount. Ebott. A mountain known to have taken many children. You...You need to have a really open mind for this next part…" 

The man nodded and sat on an old washer, motioning for him to continue. He took a deep breath.  
"There was a barrier that was put up a thousand years before and needed seven human souls to break. With a heavy heart and mind, their king had amassed six, his burden turning him into a shell of what he used to be. He lost his wife and his son and the daughter he'd come to see as his own. She wanted the son to take her soul and reach the surface to find help. When she ingested handfuls of buttercups, she got her wish, but with a heinous outcome. The son took her soul and merged with it, passing through the barrier to take her back to the surface to be buried. The humans thought he'd killed her and proceeded to riot after him. Though he could escape, he didn't want to hurt them, and was subsequently killed. He reformed in a scientist's lab back in the underground, but as a sentient flower with no soul. He became corrupt and found that he could reset time to a previous point. His countless resets drove him into madness. When the final human child fell, she had the same trait as the first. Determination. And the ability to save and reset was passed to her from the son, who, now, went by Flowey. This final human had a choice. Save them all. Save herself. Or succumb to the corrupt curiosity and kill them all. She had countless resets, before deciding to save them...for a final time. When they left, she spared Flowey and brought him with them to the surface...where she proceeded to destroy the reset ability she had, so that she wouldn't be tempted to go back." He was stared at with wide eyes that sparked with interest.  
"Shounen...what…"   
"I can prove it, too. I just need a vessel with the ability to project sound." He dug around in the junk and came back with an old boombox and a generator. Hooking them up, his eyes glowed a faint yellow, before he closed them and focused. The machine shuddered to life.  
"Did it work?" The hero jumped, when a flamboyant, male, voice came from the speakers.  
"Why hello, Darling!"   
"Hi, Mettaton. Sorry...It's not the most dignified…"  
"Nonsense, Dear. It's the best you could do." The lines on the front seemed to act like eyes, as they turned to the blonde.  
"Hello, Yagi-san." Blue eyes blinked rapidly.  
"Hello...You have...a very heavy American accent…"  
"Why of course! I was built in America and my coding is one hundred percent English!"   
"Built?"   
"I am a robot, Darling. A robot with a soul."   
"But...How?"   
"My creator, the brilliant Dr. Alphys, was and still is one smart cookie...eh...pun not intended. She was able to synthesize a real soul. But only a monster soul, not a human one, unfortunately."   
"You said she still is one…Is she…"  
"Oh no. She passed away a couple centuries ago. Her soul, however, was transferred to Izu-kun here, along with the rest of us. We were all in a sort of limbo, before finding ourselves pushed into him as a child. I believe he was around seven or so. Our souls and abilities, along with the souls of the eight humans, fused with his, giving him a magical core of his own and allowing him to use our abilities. Most of us have physical attacks, but Alphys didn't really. She's the source of technology knowledge he can tap into. Over the course of us being tied to him, he's been trying to find a way to let us out, so we can move again. He's figured something out for me, which is this, but not for the others yet, besides Grillby."

Toshinori rubbed his face.  
“Who are the rest?”  
“I’m Mettaton, a robot as I said. There’s the skeleton brothers, Sans and Papyrus and their dad, Gaster. Toriel and Asgore are goat monsters and are the queen and king of the monsters, respectively. There’s Undyne, a fish monster, and her wife, Alphys, a lizard monster and the royal scientist after Gaster died. Muffett is a spider monster and Grillby is a fire elemental monster. There’s one more, but he’s kept locked away, since contact with the soul of Determination causes him to go corrupt. His name is Asriel and was the son in Izuku’s retelling of monster history...Our ambassador, Frisk, can form from the soul of Determination fairly easily, but she’s the only thing keeping the other half from corrupting it. The other girl...The first fallen human in the story. Chara was corrupted by vengeance and hatred, warping the sense of determination into one more of spite. Frisk keeps her in check. I know this all sounds like rubbish, but I’m sure you’ve heard the music by now. When Izuku uses our powers, a certain song is played. That’s our themes. It happens when we’d engage in battle and even we don’t know where it comes from.” Izuku nodded.  
“The first one you probably heard, from the slime villain a couple months ago. The first one was Megalovania. Sans’ theme. Then Spear of Justice from the second time, as I used Undyne’s abilities. The third song was a mix of the two, we call Spear of Karma, since it mixes both of their abilities together. I can’t fuse two of them together for long periods of time, though." 

Mettaton looked back to Izuku.  
"Hun...Looks like the connection's slipping. You should let go, so you don't get hurt again." The boy nodded and the boombox fell silent again, as Izuku turned back to his teacher. Toshinori looked awed. Like his eyes had been opened.   
"Shounen...is there an easy way to bring this Grillby person out?"   
"I need a fire. Any is fine, but preferably at least palm size." The blonde pat over himself and pulled out an old lighter.  
"This is all I have…"  
"Why do you…"   
"For emergencies. You never know when you might need it." He handed it over and the boy opened it with a flick, scratching the wheel a couple times, before a flicker came to life. An orangish glow surrounded the entire thing, until two dots of pale yellow opened on the flame itself. Another second went by and they were covered by square glasses.  
"Hi, Grillby." Whatever the hero was expecting, it wasn't the soft and calm voice that came from the fire monster.  
"Hello, Izuku. Mettaton told us you brought him out. I had a feeling you'd call me." His voice was slightly deep and kind, yet portrayed his many years of wisdom. His head turned towards the blonde, as he bowed his head.  
"Good afternoon, Yagi-san."  
"Hello."  
“My name is Grillson Flambel, but I’m called Grillby by everyone. I’m a fire elemental, as Mettaton explained, and am the only other monster that Izuku can bring out into being.” The blonde nodded, as Grillby disappeared again and the lighter was handed back.  
“Interesting...Training these abilities may help you bring more of them out, if you find the right mediums.” Training would be interesting indeed.


End file.
